Heat conductive device

ABSTRACT

The present invention relates to a thermally conductive device ( 1 ) which is intended to establish mechanical and thermal contact between a first body ( 2 ), such as an electric and/or electronic circuit, and a second body ( 31 ), such as a cooling body, for the purpose of smoothing-out a temperature gradient occurring between the first and the second body. The device includes a first and a second contact pad ( 11, 12 ) and an element ( 13 ) acting therebetween. The first contact pad ( 11 ) is adapted for coaction with the first body ( 2 ) and the second contact pad ( 12 ) is adapted for coaction with the second body ( 31 ). The element ( 13 ) has at least one region ( 63   a ) that has a specific bending resistance. The region or region-proximate parts have a thermal conductance which is slightly lower than the thermal conductance of the region ( 5 ) located adjacent the region-proximate parts.

FIELD OF INVENTION

The present invention relates to a thermally conductive device formechanical and thermal contact between a first body, such as an electricand/or an electronic circuit, and a second body, such as a cooling body.

The object of this contact is to smooth-out any temperature gradientsthat may occur between the first and the second bodies, by conductingheat from the first body to the second body.

The device includes a first and a second contact pad and a resilient orflexible element acting therebetween.

The first contact pad is adapted for coaction with a first contactsurface of the first body, the second contact pad is adapted forcoaction with a second contact surface of the second body and theresilient or flexible element is intended to adapt to variations in thedistance or spacing between the two bodies that occur as result oftemperature variations in time, while retaining thermal contacttherebetween.

When the temperature of the first body is higher than the temperature ofthe second body, heat can be conducted from the first body to the firstcontact pad, via the thermal contact between said first body and saidfirst contact pad, and from the first contact pad to the second contactpad via the intermediate resilient or flexible element, and from thesecond contact pad to the second body via the thermal contact betweenthe second contact pad and the second body.

The present invention relates to a thermally conductive device which isparticularly adapted to function between an electric and/or electroniccomponent that is mounted in the proximity of a cooling body, such asinside a metal cassette, and/or in the proximity of a cooling body, suchas a cooling flange, wherein the device is intended to conduct heat fromthe component to the cassette wall and/or the cooling flange.

BACKGROUND OF THE INVENTION

So that the prior art relevant to the present invention may be morereadily understood, the known prior art will be described in twodifferent aspects.

In a first aspect, in which a hot and a cold body are related to oneanother such that a thermally conductive device acting therebetween isable to coact with respective bodies through the medium of mutuallyfacing contact surfaces, and such that the thermally conductive devicecan be clamped in between the two bodies.

A second aspect relates to the same situation, although with thedifference that the contact surfaces do not face towards one another andthe thermally conductive device cannot be clamped between the twobodies.

The first aspect of the known prior art will be described first.

It has long been known to conduct heat from a hot body to a cold bodythrough the medium of some type of thermally conductive device whichapplies a force against both the hot and the cold body.

When applying the present invention, it is important that the thermallyconductive device applies a force between the component and the coolingbody that is adapted to the mechanical strength of the circuit board, sothat the combined force exerted by a plurality of thermally conductivedevices will not result in deformation of the circuit board and to thedetriment of the circuit board components or to the actual connectionsof said mounted components. For instance, a circuit board that includessurface-mounted components is particularly sensitive to mechanicalinfluences wherewith circuit board deformation may result in total orpartial release of the solder with which the legs of the surface-mountedcomponents are affixed to the circuit board.

It is also important that the force exerted by the thermally conductivedevice between the component and the cooling body will not actdetrimentally on the cooling body. For instance, when the cooling bodyis a cassette wall, the force must be adapted to the mechanical strengthof said wall, while taking into account the fact that several suchdevices will act against the same wall and ensuring that the total forceexerted by said devices will not result in detrimental deformation ofthe wall.

It has long been known to allow the heat that radiates from box-enclosedelectronic components to be transferred from respective components tothe box walls through the medium of the air gap present between thecomponents and the box. This method is useful with components thatradiate very small quantities of heat.

It is also known to fabricate a circuit board, on which components aremounted, in mechanical and thermal contact with one of the box walls, sothat heat will be conducted from the components to the circuit board andfrom there to the box. In this case, however, it is necessary that oneside of the circuit board is free from components. Neither is it alwaysdesirable to conduct heat from the components down into the circuitboard.

It is also known to use different types of filling material between theair gap present between components and box. This application requiresthe use of some type of thermally conductive filling material. Rubberdiscs or rubber plates are one example of such filling materials.Although rubber discs or plates are effective, they require a very highcontact pressure in order to fill the air gap satisfactorily. It is alsoknown to use a very soft rubber-like material that can be brought todesired shapes that are effective in filling irregular air gaps. Thismaterial, however, has a much lower thermal conductivity.

Liquid filled plastic pads are another example of such fillingmaterials, although such pads have a limited useful life and efficacy.

Foam material filled with liquid metal is still another example of suchfilling materials. This solution is highly expensive, however.

Thermally conductive filling materials and double-sided adhesive tapesare marketed by Chomerics, Inc., U.S.A., Thermagon, Inc., U.S.A. and TheBergquist Co., U.S.A., for instance.

It is also previously known to press between electric components aresilient device that will function to conduct heat from respectivecomponents to a cooling body. Different examples of this solution areillustrated in publications U.S. Pat. No. 4,674 005, DE-A1-4 324 214 andEP-A1-0 668 715.

Publication EP-A-0 151 068 describes a cooling system which includes,among other things, a heat transfer device that is in contact with thecomponent to be cooled.

The heat transfer device is pressed against the component via athermo-deformable or thermo-compressible non-rigid bellows-type devicesuch as to transport a coolant. This coolant transports heat from theheat transfer device into a cooling system.

The cooling system also includes a conduit means through which thecoolant flows, and a cooling module which functions to cool the coolant.

The non-rigid device may also include a spring which functions to pressthe heat transfer device against the component.

Other publications that disclose devices that can be considered to formpart of the known prior art are publications SE-B-0 433 021 and EP-A-0541 456.

The known prior art according to the second aspect will now bedescribed.

It is known to mount a cooling body, such as a cooling flange on or inthe vicinity of a circuit board on which hot bodies, such as electricand/or electronic components, are mounted. A cooling “flange” may alsobe comprised of one side of a cassette in which the circuit board withcomponent is mounted.

In these cases, the cooling flange will often be positioned so that itscontact surface does not lie immediately above the body to be cooled,and consequently it is not possible to clamp a thermally conductivedevice between the two bodies in a natural manner so to speak.

It is also known in this second aspect of the prior art to use differenttypes of filling material, although this is difficult to achieve byvirtue of the fact that the material cannot be clamped in between thetwo bodies.

It is also known to fasten between a cooling flange and a componenttongue-shaped strips that function to conduct heat from the component tothe cooling flange.

These strips may be comprised of a plurality of mutually superimposedfoils which are slidably fastened at one body, or at both bodies, toallow a height variation between the two bodies caused by variations intemperature, for instance.

With the intention of enabling the present invention to be understoodmore thoroughly and with the intention of simplifying the description ofthe present invention, the following expressions are used in thedescription and Claims.

Thermal resistivity and thermal conductivity are used synonymously anddescribe the ability of a certain material to conduct heat.

Thermal resistance and thermal conductance are used synonymously anddescribe a total absolute value of the ability of a device to conductheat, and are determined by the thermal resistivity or thermalconductivity of the material included in the device, and thedimensioning of said device.

When a device is comprised of a material that has a certain thermalconductivity and that is not fully determined with respect to itsdimensions, this is defined by the expression thermal conductance. Thisexpression can be illustrated, for instance, by the fact that thethermal conductance of a cylinder comprised of a given material andhaving a diameter of 2 cm will be higher than the thermal conductance ofa cylinder of the same material but having a diameter of 1 cm.

The total thermal resistance of the cylinder is not determined bydiameter alone, since the length of the cylinder and the thermalresistivity or thermal conductivity of the material must also be knownin order to determine this parameter. Nevertheless, it is possible todiscuss the thermal conductance of a device, or part of a device, on thebasis of a limiting dimension, such as the diameter of a cylinder,without having knowledge of all dimensions or of the thermal resistivityor thermal conductance of the material.

SUMMARY OF THE INVENTION TECHNICAL PROBLEMS

With respect to a thermally conductive device that is intended toestablish mechanical and thermal contact between a first body, such asan electric and/or electronic circuit, and a second body, such as acooling body, with the intention of smoothing-out occurrent temperaturegradients between the first and the second body, comprising a first anda second contact pad and a resilient element acting therebetween,wherein the first contact pad is adapted for coaction with a firstcontact surface belonging to the first body, the second contact pad isadapted for coaction with a second contact surface belonging to thesecond body, wherein the first and the second body are positioned inrelation to one another so that the two contact surfaces will facetowards one another, and wherein the resilient element is adapted toexert a predetermined pad-separating force against the first and thesecond contact pad respectively such that said pads will press againstrespective first and second bodies, it will be seen when considering theearlier state of the art that a technical problem resides in the abilityto design the resilient element so that it will exhibit an adapted highdegree of compressibility that is representative of the predeterminedforce, at the same time as the device exhibits in total an adapted highthermal conductance.

Another technical problem is one of realizing how a thermally conductivedevice shall be designed to enable it to be compressed and expandedrespectively in response to variations in the distance between the firstand the second body, e.g. variations due to temperature variations orchanges in the vertical dimensions of components for instance.

It will also be seen that a technical problem resides in providing athermally conductive device that is of very simple construction but isnevertheless able to solve these technical problems.

Another technical problem is one of realizing how an attached rod shallbe designed to afford a high thermal conductance and, at the same time,have a very low bending resistance to a force that acts laterally inrelation to the longitudinal axis of the rod.

It will also be seen that a technical problem resides in realizing howknowledge of the thermal conductance and the bending resistance of a rodcan be used in the construction of a thermally conductive device.

Another technical problem is one of realizing the advantages that areafforded by a device in which the resilient element includes at leastone resilient configuration wherein each resilient bent region in theresilient configuration is allocated a specific bending resistance and aspecific thermal conductance.

Another technical problem is one of realizing the possibilities that areafforded when one bent region can be given a bending resistance and/or athermal conductance that deviates from the bending resistance and/or thethermal conductance of one or several other bent regions.

Another technical problem is one of realizing how a device shall bedesigned in order to enable it to be produced readily in the form of asingle bar.

Yet another technical problem is one of realizing the technicalmanufacturing advantages that are afforded when respective bent regionsare comprised of a material-thinning groove, where respective bentregions may consist of a permanently bent region.

It will also be seen that a technical problem resides in dimensioningthe bar and the material-thinning grooves provided therein such as toobtain a predetermined low bending resistance in each bent region and apredetermined high thermal conductance with respect to the thermallyconductive device.

A further technical problem is one of realizing the manufacturingadvantages that are obtained when the device is comprised of plateswhere the bent regions are comprised of a foil bridge and where the foilis bent or curved between the plates in a manner to form said thermallyconductive device.

It will also be seen that a technical problem resides in adapting thedimensions of the plates and the foil bridges and also the distancebetween two mutually adjacent plates such as to obtain a predeterminedlow bending resistance in each bent region, and a predetermined highthermal conductance in respect of the thermally conductive device.

Another technical problem is one of realizing how plates and one or morefoil bridges can be mutually joined in a satisfactory manner.

Still another technical problem is one of realizing the importance ofthe ability of the device to take-up deviations in parallelism betweentwo bodies while retaining the desired high thermal conductance of thedevice and the low bending resistance in the bent regions, essentiallyirrespective of the embodiment concerned.

Another technical problem is one of realizing how a device shall beconstructed to take-up such deviations in parallelism between the twobodies.

It will also be seen that a technical problem resides in realizing theconditions required to prevent adjacent legs from contacting one anotheras bending occurs in said bent region, when using a material-thinninggroove or a foil bridge in said bent region.

It can also be considered problematic to realize how to avoid mutualcontact between two adjacent legs as a result of a bend in said bentregion.

Another technical problem resides in the choice of a suitable materialfor the bar, the plates and the foil bridges.

It will also be seen that a technical problem resides in realizing how aplurality of thermally conductive devices can be applied between aplurality of cassette-mounted components and the inner surface of acassette wall.

With respect to a thermally conductive device that is intended to makemechanical and thermal contact between a first body, such as an electricand/or electronic circuit, and a second body, e.g. a cooling body, inorder to smooth-out any temperature gradients that may occur between thefirst and the second bodies, such as to conduct heat from the first bodyto said second body, and which comprises a first and a second contactpad and a resilient element acting therebetween, wherein the firstcontact pad is adapted for coaction with a first contact surfacebelonging to said first body, said second contact pad is adapted forcoaction with a second contact surface belonging to said second body,wherein said two bodies are positioned mutually so that said two contactsurfaces will essentially face in mutually the same direction, andwherein said flexible element is adapted to allow relative perpendicularmovement between said first and said second contact surfaces whileretaining the coaction between said first contact pad and said firstsurface and the coaction between said second contact pad and said secondcontact surface, it will be seen when considering the prior art that atechnical problem resides in designing the flexible element so as toexhibit an adapted low bending resistance while the device exhibitstotally an adapted high thermal conductance.

Another technical problem is one of realizing how a thermally conductivedevice shall be designed in order to enable it to bend or curve inresponse to variations in the distance between the first and the secondbodies, such as variations due to temperature variations or varyingcomponent heights.

It will also be seen that a technical problem resides in providing athermally conductive device of very simple construction that is able tosolve these technical problems.

Still another technical problem resides in realizing the advantages thatare associated with a device in which each bendable region in saidbendable element is allocated a specific bending resistance and aspecific thermal conductance.

It will also be seen that a technical problem resides in realizing thepossibilities that are afforded by providing a bendable region with abending resistance and/or a thermal conductance that differs from thebending resistance and/or the thermal conductance of one or more otherbendable regions.

Another technical problem is one of realizing themanufacturing/technical advantages that are afforded when the device iscomprised of a bar in which respective bendable regions are comprised ofrespective material-thinning grooves.

Still another technical problem is one of being able to adapt thedimensions of a bar and the material-thinning grooves provide therein ina manner to obtain a predetermined low bending resistance in eachbendable region and a predetermined high thermal conductance in respectof said thermally conductive device.

Yet another technical problem is one of realizing the manufacturingadvantages that are obtained when the device is comprised of plates andthe bendable regions are comprised of foil bridges.

It will also be seen that a technical problem is one of realizing thesignificance of adapting the dimensions of plates and foil bridges thatare used and the distance between two mutually adjacent plates such asto obtain a predetermined low bending resistance in each bendable regionand a predetermined high thermal conductance in respect of the thermallyconductive device.

It will also be seen that a technical problem resides in realizing theconditions required to prevent adjacent legs from contacting one anotheras bending occurs in said bendable region, when using amaterial-thinning groove or a foil bridge in said bendable region.

It will also be seen that a technical problem is one of realizing howthe thermal conductance can be increased with the use of thickermaterial without at the same time increasing the bending resistance by acubic ratio to thickness, irrespective of which embodiment of thepresent invention is used.

SOLUTION

With the intention of solving one or more of the aforesaid technicalproblems, the present invention takes as its starting point a thermallyconductive device which is operable for establishing mechanical andthermal contact between a first body, such as an electric and/orelectronic circuit, and a second body, such as a cooling body, with theintention of smoothing-out temperature gradients that occur between thefirst and the second body, by conducting heat from the first body to thesecond body or vice versa.

The device includes a first and a second contact pad and a resilientelement acting therebetween.

The first contact pad is adapted for coaction with a first contactsurface belonging to the first body, the second contact pad is adaptedfor coaction with a second contact surface belonging to the second body,wherein the two bodies are mutually positioned so that the two contactsurfaces face towards one another, and wherein the resilient element isadapted to exert on the first and the second contact pads apredetermined pad-separating force that urges said pads againstrespective first and second bodies.

With a starting point from this device, the present invention proposesthat the resilient element includes at least one bent region that has abending resistance which is representative of said predetermined force,that said region or parts that are proximate to said region have athermal conductance which is slightly lower than the thermal conductanceof the region adjacent to said region proximate parts.

With the intention of obtaining a resilient element that has an adaptedhigh thermal conductance and an adapted low bending resistance, it isproposed in accordance with the invention that the resilient elementwill include at least one resilient configuration that includes a firstand a second leg, wherein a first end of the first leg is connected tothe first contact pad through the medium of a first bent region, asecond end of the second leg is connected to the second contact padthrough the medium of a second bent region, and a second end of thefirst leg is connected to a first end of the second leg through themedium of a third bent region.

The device can be made compressible and expandable with the aid of aresilient element that includes two resilient configurations that arepositioned so that all third bent regions of respective resilientconfigurations will face towards one another.

A simple way of obtaining a bent region of adapted low bendingresistance and high thermal conductance that is slightly higher than thethermal conductance of the peripheral regions, is to allow respectivebent regions to be comprised of a material-thinning groove in whichbending can take place.

This enables the device to be comprised of a single bar that includes aplurality of material-thinning grooves, thereby enabling the bar to bendor curve in said grooves and therewith form the first and the secondcontact pads and the resilient element.

It is proposed in accordance with the invention that the bar shall havea material thickness of 0.2 to 1.0 mm, preferably 0.4 to 0.6 mm, andthat the material-thinning groove shall have a material thickness of0.01 to 0.5 mm, preferably 0.05 to 0.15 mm, and that the width of thegroove shall be from 0.4 to 4 mm, preferably 0.8 to 1.2 mm. It will beunderstood that these sizes are convenient sizes and are given solely byway of example.

In order to enable the device to provide good thermal contact with anadapted low contact force even when the first and the second body arepositioned obliquely to one another, respective first and second legsmay be provided with a material-thinning groove that extends from thefirst end to the second end diagonally over respective legs, meetingeach other at the third bent region common to the first and the secondleg.

A bent region that has an adapted low bending resistance and a highthermal conductance, which is slightly higher than the thermalconductance of the peripheral regions, can alternatively be obtained byforming the first and the second contact pads and the first and thesecond legs within respective resilient configurations from platesforming the bent regions from foil bridges that are bent between theplates, thereby forming the device.

In accordance with the invention, the plates may have a materialthickness of 0.2 to 1.0 mm, preferably 0.4 to 0.6 mm, and the foilbridges may have a material thickness of 0.01 to 0.5 mm, preferably 0.05to 0.15 mm, and the distance between two adjacent plates may be 0.4 to 4mm, preferably 0.8 to 1.2 mm. It will be understood that thesedimensions are convenient dimensions and have been given solely by wayof example.

This embodiment also enables the device to establish good thermalcontact with an adapted low contact force even when the first and thesecond bodies are positioned obliquely in relation to one another, byvirtue of the fact that the plates, which form respective first andsecond legs, are divided in two from their first end to their second enddiagonally across respective legs, wherein said divisions meet oneanother at the third bent region common to said first and said secondlegs, and wherein respective two-part plates are held together by a foilbridge or tie.

The plates may be either glued or soldered to the foil bridge, forinstance.

In order to obtain a high thermal conductance, the materials used in thebar, plates or foil will conveniently possess a high thermal conductanceand a high modulus of elasticity, such as aluminum, copper or silver.

In accordance with the invention, bent regions and other parts shall bedimensioned so that the final device will have a total bendingresistance that enables the resilient element to be compressed to anextent corresponding to 1 mm, preferably 0.4 to 0.8 mm, in response toan applied force that corresponds to about 1 N, and so that the totalthermal conductance will be in the order of 5 to 15° C./W, preferablyabout 10° C./W for components that develop a power in the region of 1 W,and so that the combined force exerted by a number of devices will notdetrimentally influence the cooling body or the circuit board to whichthe various components are connected.

An inventive device may be used when the first body is an electriccomponent, such as an integrated circuit mounted on a cassette-enclosedcircuit board, wherein the cassette is comprised of a bottom part and acover member and wherein the second body is comprised of said covermember.

With the intention of enabling and simplifying mounting of one or morethermally conductive devices between one or more components within acassette and the cassette cover, it is proposed in accordance with theinvention that the mechanical contact between the second contact pad andthe cover is achieved through the medium of a mechanically fixed andthermally conductive contact. This enables the cover member to be liftedto provide access to the circuit board and its components with thethermally conductive devices remaining seated on the cover member.

The fixed mechanical contact may be implemented by soldering or gluing.

Further suitable embodiments of the present invention that solve some ofthe aforesaid technical problems are achieved on the basis of athermally conductive device intended for establishing mechanical andthermal contact between a first body, such as an electric and/orelectronic circuit, and a second body, such as a cooling body, with theintention of smoothing-out a temperature gradient occurring between thefirst and the second body.

The device includes a first and a second contact pad and a bendableelement acting therebetween, wherein the first contact pad is adaptedfor coaction with a first contact surface belonging to the first body,the second contact pad is adapted for coaction with a second contactsurface belonging to the second body, and wherein the bodies arepositioned relative to one another such that the two contact surfaceswill face essentially in mutually the same direction.

The bendable element is adapted to afford relative perpendicularmovement between the first and the second contact surfaces whilemaintaining coaction between the first contact pad and the first contactsurface and between the second contact pad and the second contactsurface.

It is proposed in accordance with the invention that in respect of adevice of this kind, the resiliently bendable element shall have atleast one bendable region that has an adapted bending resistance.

This region or parts in the close proximity thereof are given a thermalconductance that is slightly higher than the thermal conductance ofregions that lie adjacent to the region-proximate parts.

The resilient element includes at least one leg, wherein a first end ofsaid leg is connected to the first contact pad through the medium of afirst bendable region, and a second end of said leg is connected to thesecond contact pad through the medium of a second bendable region.

It is also proposed in accordance with the invention that the firstbendable region may have a bending resistance and/or a thermalconductance that differs from the bending resistance and/or thermalconductance of the second bendable region.

In one embodiment of the invention, respective bendable regions arecomprised of a material-thinning groove.

The device may conveniently be comprised of a single bar that includes aplurality of material-thinning grooves.

According to the invention, the bar may have a material thickness of 0.2to 1.0 mm, preferably 0.4 to 0.6 mm, the material-thinning groove mayhave a material thickness of 0.01 to 0.5 mm, preferably 0.05 to 0.15 mm,and the width of the material-thinning groove may have a width of 0.4 to4 mm, preferably 0.8 to 1.2 mm. It will be understood that thesedimensions are convenient dimensions and are given solely by way ofexample.

In order to enable the thermally conductive device to compensate fordifferent disparities in the parallelism between the two bodies, it isproposed in accordance with the invention that the leg is provided witha material-thinning groove that extends from the first end to the secondend of said diagonally across the leg.

The device may also conveniently be comprised of plates and one or morefoils bridges or ties, wherein the first and the second contact pads andsaid legs are comprised of plates, and respective bendable regions arecomprised of foil bridges or ties.

It is proposed in accordance with the invention that the plates willhave a material thickness of 0.2 to 1.0 mm, preferably 0.4 to 0.6 mm,that the foil bridges will have a material thickness of 0.01 to 0.5 mm,preferably 0.05 to 0.15 mm, and that the distance between two mutuallyadjacent plates will be 0.4 to 4 mm, preferably 0.8 to 1.2 mm. It willbe understood that these dimensions are convenient dimensions and thatthey have been given solely by way of example.

The device can also in this case be adapted to compensate fordisparities in parallelism, by dividing the leg-forming plate into twoparts from the first end to the second end diagonally across the leg,said two-part plate being held together by a foil bridge or tie.

A device of the aforedescribed kind is particularly useful when thefirst body is a circuit board mounted electric component, such as anintegrated circuit, and when the second body is a cooling body, such asa cooling flange, that is mounted in the proximity of or on a circuitboard.

According to one embodiment of the invention, the mechanical contactbetween the first contact pad and the first body is a mechanically fixedand thermally conductive contact, and the mechanical contact between thesecond contact pad and the second body is a slidable mechanical andthermally conductive contact.

With the aim of enabling at least the thermal conductance of a device tobe increased without, at the same time, increasing the bendingresistance by more than the same extent to which the thermal conductanceis increased, it is proposed that a plurality of parts of the device, ora plurality of devices, shall be connected in parallel as an alternativeto increasing the thickness of the material in the thinning region.

ADVANTAGES

Those advantages that are primarily characteristic of an inventivethermally conductive device reside in enabling the provision, in asimple manner, of a device that achieves between a hot and a coolingbody a mechanical and flexible thermal contact with an adapted thermalconductance and an adapted contact force, thereby enabling heat to betransferred effectively from the hot body, which may comprise circuitboard mounted electric and/or electronic components, to the cooling bodywithout heating the circuit board or adjacent components and without theforce acting between a number of components and the cooling body havinga detrimental effect on either the cooling body or the circuit board.

The main characteristic features of an inventive thermally conductivedevice are set forth in the characterizing clause of the following Claim1 and also in the characterizing clause of the following Claim 28.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of exemplifying embodiments of thermally conductive deviceshaving properties that are significant to the present invention will nowbe described in more detail with reference to the accompanying drawings,in which

FIG. 1 illustrates schematically the transfer of heat from a hot body toa cold body through the medium of a thermally conductive device;

FIG. 2 illustrates in perspective a frame that carries a plurality ofcassettes, of which one is shown in a partially broken view, and acircuit board mounted in this cassette;

FIG. 3 is a side view and sectional view of a cassette that includes acircuit board and a number of components connected thereto;

FIGS. 4A, 4B and 4C are schematic illustrations of different casesrelating to the influence of a force on the free end of a rod whoseother end is fixedly attached;

FIG. 5 is a side view of a thermally conductive device that is operativebetween a first and a second body;

FIG. 6 is a detailed illustration of the distribution of differentregions in and around a bent region;

FIG. 7 is a schematic illustration of the construction of a resilientconfiguration;

FIG. 8 illustrates in perspective one possible embodiment of a bentregion;

FIG. 9 illustrates in a simplified fashion the manner in which athermally conductive device can be formed from a bar;

FIG. 10 illustrates possible distributions of material-thinning groovesalong a bar;

FIG. 11 illustrates part of a permanently bent bar that includesmaterial-thinning grooves according to FIG. 10;

FIGS. 12A, 12B and 12C illustrate in a simplified fashion a plurality ofdifferent possible splicing points on a bar in the construction of athermally conductive device;

FIG. 13 illustrates in perspective another possible embodiment of a bentregion;

FIG. 14 illustrates in simple fashion the manner in which a device canbe formed from a plurality of plates and a foil bridge or tie;

FIG. 15 illustrates the manner in which a length-adapted foil tie isable to bind a number of plates together;

FIG. 16 illustrates a possible foil-tie distribution between plates;

FIG. 17 illustrates part of an arrangement comprising plates and foilties according to FIG. 16;

FIG. 18 illustrates schematically a first type of deviation inparallelism between two bodies;

FIG. 19 illustrates schematically a second type of deviation inparallelism between two bodies;

FIG. 20 illustrates a possible distribution of parts on a bar with theintention of compensating for deviation in parallelism between twobodies in accordance with FIGS. 18 and 19;

FIG. 21 is a side view of a device that includes four resilientconfigurations;

FIG. 22 is a side view of a device that includes only one resilientconfiguration;

FIG. 23 illustrates schematically possible transfer of heat from onebody to another body through the medium of a thermally conductivedevice;

FIG. 24 is a side view of a thermally conductive device in coaction witha first and a second body;

FIG. 25 is a detailed illustration of a bendable region with adjacentparts and regions;

FIG. 26 illustrates a first embodiment of a thermally conductive deviceaccording to FIG. 23;

FIG. 27 illustrates a second embodiment of a thermally conductive deviceaccording to FIG. 23;

FIG. 28 illustrates a further embodiment of a thermally conductivedevice according to FIG. 26;

FIG. 29 illustrates a further embodiment of a thermally conductivedevice according to FIG. 27;

FIG. 30 illustrates schematically a first type of deviation inparallelism between two bodies;

FIG. 31 illustrates schematically a second type of deviation inparallelism between two bodies;

FIG. 32 illustrates a possible distribution of bendable partisions withthe intention of compensating for a deviation in parallelism between twobodies in accordance with FIGS. 30 and 31;

FIG. 33 illustrates schematically variations in the height or verticaldimension of one body in relation to another body;

FIG. 34 illustrates possible attachments for fastening respectivecontact pads to respective bodies; and

FIG. 35 illustrates an embodiment in which two thermally conductivedevices are connected mutually in parallel.

DETAILED DESCRIPTION OF EMBODIMENTS AT PRESENT PREFERRED

FIG. 1 is a highly schematic illustration that shows how heat from a hotbody 2 is transferred from the hot body to a cold body 3 through themedium of a thermally conductive device 1. The thermally conductivedevice has a certain thermal conductance between the hot and the coldbodies, which, expressed simply, is given by the thermal resistivity ofthe material from which the device is made, the dimensions of thismaterial, and the thermal contact between the device 1 and therespective hot and cold bodies 2, 3.

In order to achieve the highest possible thermal conductance between thehot and the cold body 2, 3, it is endeavored to find a device that willprovide a high thermal conductance while also achieving good thermalcontact with respective hot and cold bodies.

The thermally conductive device of the FIG. 1 embodiment acts betweentwo contact surfaces, a first contact surface 2 a belonging to the firstbody 2, and a second contact surface 3 a belonging to the second body.The two bodies 2, 3 are positioned in relation to one another so thatthe two contact surfaces 2 a, 3 a face towards each other.

For good thermal contact, the device 1 may be fixedly connected torespective bodies 2, 3, fixedly connected to only one body, or looselyclamped between the two bodies.

When the device 1 is fixedly connected to only one body or is clampedbetween the two bodies 2, 3, it is necessary for the device 1 to actwith a given mechanical force between said two bodies 2, 3 in order toachieve good mechanical and therewith good thermal contact.

The present invention is based on a thermally conductive device 1 thatis either fixedly connected to solely one body or is clamped firmlybetween said two bodies 2, 3.

Such is often the case when the hot body 2 is comprised of an electricand/or an electronic component and the cold body 3 is comprised of acooling flange or of a part of a casing positioned immediatelythereabove but not in mechanical contact with said component, so as toenable ready access to the component for servicing or test measuringpurposes, for instance.

FIG. 2 illustrates a plurality of hot bodies 2 in the form of electricand/or electronic components 2, 2′ connected to a circuit board 4.

It is normal to mount a large number of circuit boards in a stand orframe 5, where respective circuit boards 4 are mounted in a cassette 3that functions as a cold body 3.

The purpose of a cassette 3 is to prevent the spread of electromagneticdisturbances and to protect against incoming electromagneticdisturbances, moisture, dirt, grease, dust and other contaminants.

Components 2 that develop heat and that are fully enclosed in this wayneed to be cooled. The cooling of cassette enclosed components isrelatively difficult to achieve. A natural method in this regard is toconduct the heat from the components 2, 2′ to the cassette casing 31 inaccordance with the FIG. 3 embodiment.

This will result, however, in heating of the cassette, which then needsto be cooled. Cooling of the cassette can be achieved by providingbetween the cassettes gaps in which a coolant, normally air, is allowedto circulate, or by mounting cooling bodies on the frame surfaces and/oron the free end-wall of the cassette.

For the purpose of conducting heat from a component 2 to the cassettecasing 31, it is normal to fill the air gap located between a component2 in the casing 31 with some type of thermally conductive device 1.

Because a circuit board 4 is able to carry a large number of components2, 2′, there is a need to use a large number of thermally conductivedevices 1, 1′ which are each able to apply between the component 2 andthe casing 31 a force that will establish good mechanical and goodthermal contact between the device, component and casing respectively.

A large number of components 2, 2′ will often be mounted on a circuitboard 4, and when several of these components need to be provided with athermally conductive device 1, 1′, the combined force exerted by saiddevices against said components may be so great as to result indeformation of the circuit board 4. For instance, this combined forcemay result in damage to components, fracturing of circuit boardconductor parts or in damage to the solder with which the componentcontacts are affixed to the circuit board. The fastenings ofsurface-mounted components are particularly sensitive in this regard.

Because the cassette walls are often very thin, in the order of 1 mm,and are made of soft material, aluminum, the combined force from thethermally conductive devices 1, 1′ may result in deformation of thecassette casing 31, cause the casing to bulge, which may mean in theworst case that the cassette 3 will not fit into its intended place inthe frame 5.

The object of the present invention is to provide a mechanicallyflexible thermal contact between a hot body and a cold body through themedium of a contact element that has a small contact force and that isable to conduct heat away from components that develop heat in the orderof 1 W.

In principle, there is nothing to prevent the present invention beingused for cooling components that develop more heat than components inthe order of 1 W. Such a device, however, would require totallydifferent dimensions to those recited in this specification.

With the intention of providing a device that will generate a smallcontact force, the present invention is based on the understanding ofthe bending resistance and the thermal conductance that is afforded by abar that is securely fixed at one end.

FIG. 4A illustrates a rod B that is securely fixed at one end B1 andwith which a force F_(B) is applied to the other end B2 of the rod in adirection perpendicular to the longitudinal axis of the rod. It isassumed that heat transfer takes place from the end B2 of the rod to itsend B1. The rod has a height or vertical dimension “h”.

In order to obtain the greatest possible downward bending of the rodwith a small force at said other end B2, the rod B may be thinnedlocally at a point “p”, as shown in FIG. 4B. This weakens the rod andpronounced downward bending of the rod will occur in response to anapplied force F_(B).

In order to ensure that the rod will bend or curve downwards to thegreatest possible extent in relation to the size of the thinning, thethinning is suitably positioned at a place on the rod B that takes-upthe greatest moment of force when the force F_(B) is applied. Thisgreatest moment of force is found in the first end B1 at the rodattachment, and hence it is appropriate to thin the rod at thisposition, in accordance with FIG. 4C.

The thinned region also results in a lower thermal conductance.

This detrimental effect of the thinned region on the thermal conductancecan be reduced by making the thinned region as short as possible in thedirection of the longitudinal axis of the rod and/or the height h′ ofthe rod can be increased, wherewith the thermal conductance of thenon-thinned parts of the rod will be higher than the thinned parts.These measures reduce the detrimental effect on the total thermalresistance of the rod.

The bending resistance of the rod is proportional to the height “h”raised to a power of three (h³), meaning that an increase in the height“h” by a factor of two will increase the thermal conductivity by afactor of two and increase the bending resistance by a factor of eight(2³).

It will be apparent to the person skilled in this art that anexcessively thin region will result in a much too weak construction andan excessively low thermal conductance. A predetermined bendingresistance and a predetermined thermal conductance can be obtained inrespect of the rod, by adapting the thickness of the thinned region andalso its length extension.

The bending resistance and the thermal conductance of a thinned regionare mutually connected. In simple terms, it can be said that the thermalconductance is proportional to the bending resistance.

FIG. 5 illustrates a proposed embodiment which is based on thesetheories. Thus, FIG. 5 illustrates a thermally conductive device 1 whichincludes a first and a second contact pad 11, 12 and a resilient element13 located therebetween. The first contact pad 11 is adapted forcoaction with a first body 2, the second contact pad 12 is adapted forcoaction with a second body 31, and the resilient element 13 is adaptedto exert on the first and the second contact pad a predeterminedpad-separating force for effective contact with respective first andsecond bodies and therewith effective transfer of heat from the first tothe second body.

As illustrated in FIG. 6, the resilient element 13 includes at least onebent region 62 that has a bending resistance which is representative ofthe predetermined force. The region 62 or region-proximate parts 62′ hasor have a thermal conductance which is slightly lower than the thermalconductance of the regions 12′, 72′ located adjacent theregion-proximate parts 62′.

The bent region 62 and the region-proximate parts 62′ have a muchsmaller bending resistance than the regions 12′, 72′ adjacent theregion-proximate parts 62′, meaning that any bending caused by anapplied force will occur in this region.

FIG. 7 illustrates a resilient element which may include at least oneresilient configuration 13 a. The illustrated resilient configurationincludes a first and a second leg 71, 72, wherein a first end 71 a ofthe first leg 71 is connected to the first contact pad 11 through themedium of a first bent region 61, a second end 72 b of the second leg 72is connected to the second contact pad 12 via a second bent region 62,and a second end 71 b of the first leg 71 is connected to a first end 72a of the second leg 72 via a third bent region 63.

There is thus obtained a resilient element 13 a that includes three bentregions 61, 62, 63 that together answer for the total bending resistanceof the resilient configuration.

There is nothing to prevent a bent region being given a bendingresistance, and therewith also a thermal conductance, that differs fromthe bending resistance and the thermal conductance of one or more otherbent regions.

This enables the construction of a resilient configuration that has apredetermined total bending resistance and a predetermined thermalconductance.

Referring back to FIG. 5, there is shown a proposed embodiment of athermally conductive device 1 whose resilient element 13 is comprised oftwo resilient configurations 13 a, 13 b, wherein respectiveconfigurations are so positioned in relation to one another that thethird bent regions 63 a, 63 b of respective resilient configurationswill be directed towards one another, in between the first and thesecond contact pads 11, 12.

A region whose bending resistance is lower than the bending resistanceof peripheral regions can be achieved in many different ways.

For instance, FIG. 8 illustrates an embodiment in which respectiveregions are comprised of a material-thinning groove 6 a and respectivebent regions have the form of permanent bends.

As evident from FIG. 9, such an embodiment can be implemented byconstructing the device from one single bar 8 which includes a pluralityof material-thinning grooves 6 a, 6 b, . . . , 6 f. The bar 8 can bepermanently bent in the grooves to form the first and the second contactpad 11, 12 and the resilient configurations 13 a, 13 b.

The grooves may be milled or pressed in the bar, for instance.

In order to avoid two mutually adjacent legs coming into contact withone another as a result of bending in a material-thinning groove, andpreventing further compression of the thermally conductive device, thereis shown in FIGS. 10 and 11 an embodiment of a resilient configuration13 a in which the first and the second bent regions 61, 62 are comprisedof a material-thinning groove 6 a, 6 c that is provided on a first side8 a of the bar 8, and in which the third bent region 63 is comprised ofa material-thinning groove 6 b on a second side 8 b of the bar 8. FIG.10 illustrates the positions of the material-thinning grooves 6 a,6 b,6c on the bar 8, and FIG. 11 illustrates part of a device that includes acontact pad according to FIG. 10.

In respect of a device according to the FIG. 8 embodiment, the bar mayhave a material thickness “a” in the order of 0.2 to 1.0 mm, preferably0.4 to 0.6 mm, the material-thinning grooves may have a materialthickness “c” in the order of 0.01 to 0.5 mm, preferably 0.05 to 0.15mm, and the material-thinning grooves may have a width “d” thatcorresponds to 0.4 to 4 mm, preferably 0.8 to 1.2 mm.

The bar regions that are to constitute the bent regions may beorientated in the bar so that the bar extremities will be splicedtogether in different ways when constructing the device.

FIG. 12A shows an embodiment in which the splice 8 c is placed in thecentre of the second contact pad 12, FIG. 12B shows an embodiment inwhich each end of the plate 8 has a size which corresponds to the sizeof the second contact pad 12 and where said end 12′ and said pad 12 aresuperimposed, and FIG. 12C illustrates an embodiment in which the splice8 c′ is placed in the centre of one leg 72 of one of the resilientconfigurations 13 a.

FIGS. 13 and 14 illustrate an embodiment in which one bent region has asmaller bending resistance than its peripheral regions. This has beenachieved by constructing the first and the second contact pads 11, 12and the first and the second legs 71, 72 in respective resilientconfigurations from plates 9 a, 9 b, . . . , 9 f, and by constructingthe bent regions from foil bridges or ties 9, with respective foilbridges being bent or curved between the plates such as to form saidthermally conductive device.

In respect of a device according to this embodiment, the plates may havea material thickness “a′” in the order of 0.2 to 1.0 mm, preferably 0.4to 0.6 mm, the foil 9 may have a material thickness “c′” in the order of0.01 to 0.5 mm, preferably 0.05 to 0.15 mm, and the distance “d′”between two adjacent plates may be 0.4 to 4 mm, preferably 0.8 to 1.2mm.

The plates 9 a, 9 b, . . . , 9 f may be fastened to the foil 9 as bygluing or soldering, for instance.

The plates 9 a, 9 b, . . . , 9 f may conveniently be formed from a bar8′ in which slots 6 a, 6 b, . . . , 6 e have been punched, in accordancewith FIG. 15, and a foil bridge or tie 9 fastened to one side of theplate 8′. Subsequent to fastening the foil bridge, the side parts 8′c,8′d of the bar are punched or stamped-out, so as to leave solelyindividual plates 9 a, 9 b, . . . , 9 f, these plates beinginterconnected by the foil bridge or tie 9.

It is also possible to use individual plates of adapted size and applythese plates to a foil bridge or tie.

In the embodiment illustrated in FIG. 15, the foil bridge or tie 9 isconveniently somewhat longer 9′ than the total length of the plates andthe adapted spacing therebetween, so as to overlap slightly whenassembling the device.

A further simplified method of constructing a device with the aid offoil bridge or tie would be to use a foil bridge that has an adhesiveside, such as a pre-glued side.

In order to prevent two mutually adjacent plates coming into contactwith one another on a bending occasion and further compression of thethermally conductive device, FIGS. 16 and 17 illustrate an embodiment ofa resilient configuration 13 a in which the first and the second bentregions 61, 62 are comprised of a foil tie 91, 92 which holds togetheradjacent plates 9 a, 9 b; 9 c, 9 d on a first side of the plates, and inwhich the third region 63 is comprised of a foil tie 93 which holdstogether adjacent plates 9 b, 9 c on a second side of said plates.

It is not unusual that parallelism between the hot and the cold bodywill deviate to some extent, such as between a component and a cassettecasing. In order to obtain good thermal contact and a desired highthermal conductance, it is important that no air wedges are presentbetween the heat conducting device and the hot or the cold body. Thethermally conductive device is able to compensate for certain deviationsin parallelism between the two bodies, but not for all types ofdeviations and not for deviations of all magnitudes.

FIG. 18 illustrates the type of deviation in parallelism that causes oneresilient configuration 13B to be compressed to a greater extent thanthe other resilient configuration 13 a. This type of deviation can bereadily compensated for by the thermally conductive device 1.

FIG. 19 illustrates another type of deviation in parallelism thatrequires an individual resilient configuration 13 b to be compressed toa greater extent at its viewerdistal end 13 b′ than at itsviewer-proximal end 13 b”. Only a small degree of compensation can bemade for this type of deviation in parallelism, without adapting thedevice particularly for this purpose.

It will be understood that the deviations in parallelism between a firstand a second body illustrated in FIGS. 18 and 19 have been greatlyexaggerated with the intention of illustrating the types of deviationsthat can occur in this respect.

It will be evident to the person skilled in this art that a deviation inparallelism between the first and the second body will not have thecultivated form of the deviation illustrated in FIG. 18 or the deviationillustrated in FIG. 19, but will normally be comprised of a combinationof the two deviations illustrated in the Figures, wherein one suchdeviation may possibly be more pronounced than the other.

With the intention of enabling the thermally conductive device tocompensate for deviations according to FIG. 19 to a great extent, thereis proposed in accordance with the invention an embodiment according toFIG. 20, in which respective first and second legs 71, 72 of respectiveresilient configurations 13 a have a partition 71 ab, 72 ab that extendsfrom the first end 71 a, 72 a to the other end 71 b, 72 b, diagonallyacross respective legs 71, 72, where the two partitions 71 ab, 72 abmeet each other at the third bent region 63 that is common to the firstand the second legs 71, 72.

The partitions 71 ab, 72 ab shall have a smaller bending resistance thanthe peripheral leg regions. This may be achieved with the aid of amaterial-thinning groove or by spacing apart two pads or plates andholding the pads or plates together with the aid of a foil bridge ortie, as described above with reference to the manner in which the bentregions can be implemented, with the exception that these partitions 71ab, 72 ab are not bent.

The partitions 71 ab, 72 ab enable respective legs 71, 72 to fold orgive way and therewith take up the type of deviation in parallelismbetween the first and the second body shown in FIG. 19.

The materials from which an inventive thermally conductive device ismanufactured will preferably be such as to provide the largest possibledifference between thermal conductivity and elasticity modulus, so as toobtain a desired high thermal conductance and a low bending resistancein the respective bent regions. Other parameters are, of course,material costs, wherein materials that have the aforesaid properties butare extremely expensive will nevertheless not be suitable because oftheir high price, such as noble materials, e.g. gold.

Suitable materials in this respect are metals that have a high thermalconductance, such as aluminum, copper or silver. There is nothing toprevent different parts of the device from being comprised of differentmaterials. For instance, the plates 9 a, 9 b, . . . , 9 f in the FIG. 13embodiment may be comprised of copper and the foil bridge or tie 9comprised of silver.

It will be obvious to the person skilled in this art that the inventivedevice will preferably be fabricated from material that possesses a highthermal conductance, most preferably copper, and the earlier referenceto copper, aluminum and silver also includes alloys of differentmaterials in which copper, aluminum and silver are the mainconstituents.

A possible combination that does not include metals is a thermallyconductive device moulded from plastic material and having a low bendingresistance in the bent regions and which is reinforced with carbonfibre, which has a very low thermal resistivity.

The object of one specific embodiment of the present invention is toprovide a thermally conductive device that has the following properties:The included bent regions have a total bending resistance that willresult in the compression of an included resilient element of 1 mm,preferably of 0.4 to 0.8 mm, in response to an applied force of about 1N and the total thermal conductance of which is in the order of 5 to 15°C./W, preferably about 10° C./W.

It will be evident that a thermally conductive device may include one ormore bent regions in accordance with the FIG. 8 embodiment, or one ormore bent regions in accordance with the FIG. 13 embodiment.

For the sake of simplicity, the aforesaid embodiments have includedthermally conductive devices that have two resilient configurations.

However, there is nothing to prevent a thermally conductive deviceincluding a plurality of resilient configurations 13 a, 13 b, 13 c, 13e, as shown in FIG. 21. This embodiment enables the thermal conductanceto be increased without, at the same time, increasing the bendingresistance more than necessary, since an individual thinned region thatincreases its thickness by a factor of two also increases its bendingresistance by a factor of eight. On the other hand, the bendingresistance is increased solely by a factor of two when two parallelresilient elements replace a single resilient element.

As evident from FIG. 22, a thermally conductive device may includesolely one resilient configuration 13 a.

Circuit boards 4 carrying components 2, 2′ that, according to FIG. 2,are mounted in a cassette 3 that, in turn, is inserted into a frame 5together with other cassettes, sometimes requires inspection and/orservice. It is important that the circuit board 4 can be easily reachedin such circumstances, and that the cassette 3 can be readily reclosedwhen the inspection or service is terminated.

A circuit board 4 may carry a plurality of components 2, 2′ that arecooled in accordance with the present invention, and consequently it isnecessary to fixedly fasten the thermally conductive devices to one ofthe two bodies 2, 31. This solution enables a cassette to be readilyopened and reclosed while maintaining the positions of the thermallyconductive devices 1, 1′ between the components and the cassette casing.

Turning back to FIG. 5, it will be seen that the mechanical contactbetween the second contact pad 12 and the second body 31 is comprised ofa mechanically fixed and thermally conductive contact.

This means that all thermally conductive devices 1 have a respectivefixed position in the cassette casing 31. and will always be positionedcorrectly over a component 2 when mounting in a cassette 3 a circuitboard 4 that has a specific combination of components.

This fixed mechanical contact may be achieved by soldering or gluing,for instance.

In the aforedescribed embodiments, the first and the second body arepositioned in relation to one another such that the contact surfacesthat coact with which the thermally conductive device face towards oneanother.

FIG. 23 illustrates an embodiment which shows that applications arise inwhich this is not the case. For instance, it is not unusual for a firstbody 20, such an electric and/or electronic component, to be positionedrelative to another body 30, such as a cooling flange, such that the twocontact surfaces, a first contact surface 28 belonging to the first body20 and a second contact surface 30 a belonging to the second body 30 donot face towards one another but in one and the same direction, forinstance.

This application requires a thermally conductive device 10 that is ableto coact with the two contact surfaces 20 a, 30 a.

A proposed embodiment of the invention adapted to this end is shown inFIG. 24. This Figure illustrates a thermally conductive device 10 thatincludes a first contact pad 110 which is adapted for coaction with afirst contact surface 20 a belonging to a first body 20, such as anelectric and/or an electronic component that is fixed to a circuit board40, a second contact pad 120 which is adapted for coaction with a secondcontact surface 30 a belonging to a second body 30, such as a coolingbody, for instance a cooling flange positioned in the proximity of or onthe circuit board 40, and a resiliently bendable element 130 that actstherebetween.

In the case of variations in the size of said bodies due to variationsin temperature and due to differing manufacturing tolerances in themanufacture of the bodies, it is important that the bendable element 130is able to bend so as to allow relative perpendicular movement betweenthe first and the second contact surfaces 20 a, 30 a while maintainingthe coaction between the first contact pad 110 and the first contactsurface 20 a, and between the second contact pad 120 and the secondcontact surface 30 a.

By relative perpendicular movement is meant a first movement of thefirst contact surface relative to a normal to the first contact surfaceand/or a second movement of the second contact surface relative to anormal to the second contact surface, where the first movement is not ofthe same magnitude, nor necessarily in the same direction, as the secondmovement.

In order to prevent the occurrence of stresses in one or both bodies 20,30 and/or the supportive surface 40 on which they are mounted as aresult of such movement, it is important that the bending resistance isadapted to a low value.

It is also important that the bendable element 130 has a high thermalconductance.

These criteria, a low bending resistance and a high thermal conductance,enable the theories presented with reference to FIG. 4 to be appliedalso in this case.

As evident from FIG. 25, the thermally conductive device 10 of thisembodiment shall include at least one bendable region 610 that has anadapted bending resistance and that the region 610 or region-proximatepart 610′ has a thermal conductance that is slightly higher than thethermal conductance of the regions 110′, 170′ located adjacent saidregion-proximate parts 610′.

According to FIG. 26, the bendable element 130 includes at least one leg70 and a first and a second bendable region 610, 620. A first end 70 aof the leg 70 is connected to the first contact pad 110 via the firstbendable region 610, and a second end 70 b of the leg 70 is connected tothe second contact pad 120 via the second bendable region 620.

FIGS. 26 and 27 illustrate two different ways of obtaining bendableregions in accordance with the present invention. According to theembodiment illustrated in FIG. 26, respective bendable regions 610, 620are comprised of respective material-thinning grooves 60 a, 60 b in abar 80, while according to the embodiment illustrated in FIG. 27respective bendable regions 610, 620 are comprised of a foil bridge ortie 90 and the contact pads 110, 120 and the leg 70 are comprised ofrespective plates 90 a, 90 b, 90 c.

We shall not burden the description with further details of theseembodiments, since they have been described earlier in conjunction withthe description of the bent regions of previous embodiments.

However, it can be mentioned that the bar or respective plates mayconveniently have a material thickness “a0”, “a′0” in the order of 0.2to 1.0 mm, preferably 0.4 to 0.6 mm, that the material-thinning groovesor the foil bridge or tie used may conveniently have a thickness of“c0”, “c′0” in the order of 0.01 to 0.5 mm, preferably 0.05 to 0.15 mm,and the material-thinning grooves may conveniently have a width “d” of,or the distance between two adjacent plates “d′0” of 0.4 to 4 mm,preferably 0.8 to 1.2mm.

However, it will be obvious that in order to prevent joining together ofa contact pad 110, 120 with the intermediate leg 70 when the bendableregions 610, 620 in FIG. 28 bend excessively, the first bendable region610 shall be provided with a material-thinning groove 60 a on a firstside 80 a of the bar 80 and the second bendable region 620 may beprovided with a material-thinning groove 60 b on a second side 80 b ofthe bar 80.

Correspondingly, as shown in FIG. 29, when the thermally conductivedevice is comprised of plates 90 a, 90 b, 90 c and foil bridge or ties910, 920, the first bendable region 610 is conveniently comprised of afoil bridge or tie 910 that holds together mutually adjacent plates 90a, 90 b on a first side of respective plates and the second bendableregion 620 may be comprised of a foil bridge or tie 920 that holdstogether mutually adjacent plates 90 b, 90 c on a second side ofrespective plates.

It is also necessary in the case of these embodiments that the thermallyconductive device is able to maintain good thermal contact even in theevent of errors in the parallelism between the two contact surfaces.

It will readily be seen that errors in parallelism according to FIG. 30,where the normals 20 a′, 30 a′ to the two contact surfaces 20 a, 30 amay be included by a common plane, can be readily compensated for by aninventive thermally conductive device. There is nothing to indicate thatthis type of positioning of the bodies shall be understood as an errorin parallelism, since it is quite possible that applications will occurin which the two contact surfaces have the directions shown in FIG. 30.

A deviation in parallelism of the kind illustrated in FIG. 31, in whichthe normals 20 a′, 30 a′ to the two contact surfaces 20 a, 30 a cannotbe included in a common plane, can only be compensated for to a slightextent by an inventive thermally conductive device.

In order to provide improved compensation for deviations in parallelismin accordance with FIG. 31, the leg 70 can be given a bendable region630 which extends from the first end 70 a to the second end 70 bdiagonally across the leg 70.

This bendable region 630 may, for instance, be comprised of amaterial-thinning groove, according to FIG. 26, or the leg 70 may bedivided into two with the two parts held together by a foil bridge ortie such as to form the bendable region 630 according to FIG. 27.

The bar 80 shown in FIG. 26 may conveniently be made of metal, such ascopper, aluminium or silver.

When plates and foil bridge or ties are used, in accordance with FIG.27, it may be convenient for the plates 90 a, 90 b, 90 c to be made ofcopper and the foil bridge or tie 90 to be made of silver.

FIG. 33 shows that when the perpendicular distance V_(a) between the twocontact surfaces 20 a, 30 a varies, it is necessary that one contact padis attached to the body with which it coacts by a slidable “g”mechanical, thermally conductive contact.

As illustrated in FIG. 34, one conceivable solution in this respect isto allow the mechanical contact 51 between the first contact pad 110 andthe first body 20 to be comprised of a fixed mechanical, thermallyconductive contact.

It is also conceivable for the mechanical contact 52 between the secondcontact pad and the second body 30 to be comprised of a slidable “g”mechanical, thermally conductive contact.

When wishing to increase the thermal conductance to an extent above thatwhich is obtained solely by decreasing the thickness of the thinnedregion, two or more thermally conductive devices can be connected inparallel, as illustrated in FIG. 35.

By including thermally conductive distances 14 a, 14 b between the twodevices 10 a, 10 b, there is obtained a total thermal conductance whichis half the thermal conductance afforded by one single device.

The bending resistance of the parallel-coupled device is two times thatof the bending resistance of a single device.

If the thickness of the material in the bendable regions (and in thedevice as a whole) had been doubled instead, the effect on the thermalconductivity would have been the same as that achieved with twoparallel-coupled devices, although the bending resistance would havebeen greatly increased, almost by a factor of eight, since the bendingresistance is proportional to the height cubed (h³).

It will be understood that the invention is not restricted to theaforedescribed and illustrated exemplifying embodiments thereof, andthat modifications can be made within the scope of the inventive conceptas defined in the following Claims.

What is claimed is:
 1. A thermally conductive device intended forestablishing mechanical and thermal contact between a first body and asecond body, comprising: a first and a second contact pad and aresilient element acting therebetween, wherein the first contact pad isadapted for coaction with a first contact surface on the first body,wherein the second contact pad is adapted for coaction with a secondcontact surface on the second body, and wherein the resilient element isadapted to exert a predetermined separating force on the first and saidsecond contact pads such as to urge the first and second contact padsinto contact with respective first and second contact surfaces, whereinthe resilient element includes at least one bending region having abending resistance which is representative of the predetermined force,the bending region having a thermal conductance that is lower than athermal conductance of regions of the resilient element located adjacentthe bending region, wherein the at least one bending region includes afirst bending region, a second bending region, and a third bendingregion, and the resilient element includes at least one resilientconfiguration that comprises a first and a second leg, a first end ofthe first leg being connected to the first contact pad through the firstbending region, a second end of the second leg being connected to thesecond contact pad through the second bending region; and a second endof the first leg is connected to a first end of the second leg throughthe third bending region.
 2. A device according to claim 1, wherein atleast one of the first bending region, the second bending region, andthe third bending region has at least one of a different bendingresistance and thermal conductance than another one of the first bendingregion, the second bending region, and the third bending region.
 3. Adevice according to claim 1, wherein the resilient element includes tworesilient configurations each including first, second, third bendingregions, the two resilient configurations being adapted to be disposedin relation to one another such that the third bent regions of the tworesilient configurations point towards one another between said firstand second contact pads.
 4. A device according to claim 1, wherein thefirst, second, and third bending regions include material-thinninggrooves and are permanently bendable at the grooves.
 5. A deviceaccording to claim 4, comprising a single bar provided with a pluralityof material-thinning grooves between the first and second contact padsand the first, second, and third bending regions, the bar beingpermanently bendable at the grooves.
 6. A device according to claim 5,wherein the first and second bending regions include a material-thinninggroove on a first side of said the bar and the third bending regionincludes a material-thinning groove on a second side of the bar.
 7. Adevice according to claim 5, wherein the bar has a material thickness of0.2 to 1.0 mm.
 8. A device according to claim 5, wherein thematerial-thinning groove has a material thickness of 0.01 to 0.5 mm. 9.A device according to claim 5, wherein the material-thinning groove hasa width of 0.4 to 4 mm.
 10. A device according to claim 1, wherein thefirst and second legs have a material-thinning groove that extends fromthe first end to second end of each of the first and second legs,diagonally across the first and second legs and meeting each other atthe third bending region between the first and second legs.
 11. A deviceaccording to claim 5, wherein the bar is comprised of metal.
 12. Adevice according to claim 1, wherein the first and second contact padsand the first and second legs include plates and the first, second andthird bending regions include bendable foil bridges between the plates.13. A device according to claim 1, wherein the first and second bendingregions are each a foil bridge that holds together mutually adjacentplates on a first side of the plates and the third bending region is afoil bridge that holds together mutually adjacent plates on a secondside of the plates.
 14. A device according to claim 12, wherein theplates have a material thickness of 0.2 to 1.0 mm.
 15. A deviceaccording to claim 12, wherein the foil bridge has a material thicknessof 0.01 to 0.5 mm.
 16. A device according to claim 12, wherein twomutually adjacent plates are spaced apart by a distance of 0.4 to 4 mm.17. A device according to claim 12, wherein the plates which formrespective first and second legs are divided into two parts to formtwo-part plates having divisions diagonally across the first and secondlegs from the first end to the second end, wherein the divisions meeteach other at the third bending region common to the first and saidsecond legs and the two-part plates are held together by a foil bridge.18. A device according to claim 12, wherein the plates comprise copperand the foil bridge comprises silver.
 19. A device according to claim12, wherein the plates are glued to the foil bridge.
 20. A deviceaccording to claim 12, wherein the plates are soldered to the foilbridge.
 21. A device according to claim 1, wherein the at least onebending region has a total bending resistance that enables the resilientelement to be compressed to an extent of up to 1 mm in response to anapplied force of about 1 Newton.
 22. A device according to claim 1,wherein the device has a total thermal conductance of 5 to 15° C./W. 23.A device according to claim 1, wherein the device is adapted toestablish mechanical and thermal contact between a first body, the firstbody being an electric component, and a second body, the second bodybeing a cover for the component.
 24. A device according to claim 1,wherein the second contact pad is adapted to be mechanically connectedto a second body by a fixed mechanical, thermally conductive contact.25. A device according to claim 24, wherein the fixed mechanical contactis a soldered contact.
 26. A device according to claim 24, wherein thefixed mechanical contact is a glued contact.
 27. A thermally conductivedevice intended for establishing mechanical and thermal contact betweena first body and a second body for smoothing-out a temperature gradientoccurring between the first and second bodies comprising: a first and asecond contact pad and a resilient bendable element acting therebetween,wherein the first contact pad is adapted for coaction with a firstcontact surface belonging to a first body, the second contact pad isadapted for coaction with a second contact surface belonging to a secondbody, and wherein the bendable element is adapted to allow relativeperpendicular movement between the first and second contact surfaceswhile maintaining coaction between the first contact pad and firstcontact surface and between the second contact pad and the secondcontact surface, the bendable element having at least one bendableregion having a predetermined bending resistance, the bendable regionhaving a thermal conductance that is lower than a thermal conductance ofregions of the bendable element located adjacent the bendable region,wherein the at least one bending region includes a first bending region,and a second bending region, and the bendable element includes at leastone leg, a first end of the at least one leg being connected to thefirst contact pad through a first bendable region and a second end ofthe leg being connected to the second contact pad through a secondbendable region.
 28. A device according to claim 27, wherein the firstbendable region has at least one of a bending resistance and a thermalconductance that differs from a bending resistance and a thermalconductance, respectively, of the second bendable region.
 29. A deviceaccording to claim 27, wherein the first and second bendable regionsinclude material-thinning grooves.
 30. A device according to claim 29,wherein the device includes a single bar that includes a plurality ofmaterial-thinning grooves.
 31. A device according to claim 30, whereinthe first bendable region includes a material-thinning groove on a firstside of the bar and the second bendable region includes amaterial-thinning groove on a second side of the bar.
 32. A deviceaccording to claim 30, wherein the bar has a material thickness of 0.2to 1.0 mm.
 33. A device according to claim 30, wherein thematerial-thinning groove has a material thickness of 0.01 to 0.5 mm. 34.A device according to claim 30, wherein the material-thinning groove hasa width of 0.4 to 4 mm.
 35. A device according to claim 27, wherein theat least one leg includes a material-thinning groove that extendsdiagonally across the at least one leg from said first end to saidsecond end.
 36. A device according to claim 30, wherein the bar iscomprised of metal.
 37. A device according to claim 27, wherein thefirst and second contact pads and the at least one leg are comprised ofplates and the first and second bendable regions include a foil bridge.38. A device according to claim 27, wherein the first bendable regionincludes a foil bridge that holds together mutually adjacent plates on afirst side of the plates and the second bendable region includes a foilbridge that holds together mutually adjacent plates on a second side ofthe plates.
 39. A device according to claim 37, wherein the plates havea thickness of 0.2 to 1.0 mm.
 40. A device according to claim 37,wherein the foil bridge has a material thickness of 0.01 to 0.5 mm. 41.A device according to claim 37, wherein a spacing between two mutuallyadjacent plates is 0.4 to 4 mm.
 42. A device according to claim 27,wherein the plate that forms the legs is divided into two parts from thefirst end to the second end diagonally across said legs and is atwo-part plate, the two-part plate being held together by a foil bridge.43. A device according to claim 37, wherein the plates include copperand the foil bridge includes silver.
 44. A device according to claim 37,wherein the foil bridge is glued to the plates.
 45. A device accordingto claim 37, wherein the foil bridge is soldered to the plates.
 46. Adevice according to claim 27, wherein the device has a total thermalconductance of 5 to 15° C./W.
 47. A device according to claim 27,wherein the first body is an electric component and the second body is acooling body.
 48. A device according to claim 27, wherein the firstcontact pad is adapted to mechanically contact the first body with afixed mechanical, thermally conductive contact.
 49. A device accordingto claim 27, wherein the second contact pad is adapted to mechanicallycontact the second body with a slidable mechanical, thermally conductivecontact.
 50. A device according to claim 2, wherein the resilientelement includes two resilient configurations, each resilientconfiguration including first and second legs, the conductive devicefurther including first, second, and third bending regions associatedwith each resilient configuration, the two resilient configurationsbeing adapted to be disposed in relation to one another such that thethird bent regions of the two resilient configurations point towards oneanother between said first and second contact pads.
 51. A deviceaccording to claim 2, wherein the first, second, and third bendingregions include material-thinning grooves and are permanently bendableat the grooves.
 52. A device according to claim 3, wherein the first,second, and third bending regions include material-thinning grooves andare permanently bendable at the grooves.
 53. A device according to claim4, wherein the first and second legs have a material-thinning groovethat extends from the first end to second end of each of the first andsecond legs, diagonally across the first and second legs and meetingeach other at the third bending region between the first and secondlegs.
 54. A device according to claim 5, wherein the first and secondlegs have a material-thinning groove that extends from the first end tosecond end of each of the first and second legs, diagonally across thefirst and second legs and meeting each other at the third bending regionbetween the first and second legs.
 55. A device according to claim 2,wherein the first and second contact pads and the first and second legsinclude plates and the first, second and third bending regions includebendable foil bridges between the plates.
 56. A device according toclaim 3, wherein the first and second contact pads and the first andsecond legs include plates and the first, second and third bendingregions include bendable foil bridges between the plates.
 57. A deviceaccording to claim 12, wherein the first and second bending regions areeach a foil bridge that holds together mutually adjacent plates on afirst side of the plates and the third bending region is a foil bridgethat holds together mutually adjacent plates on a second side of theplates.
 58. A device according to claim 17, wherein the plates are gluedto the foil bridge.
 59. A device according to claim 17, wherein theplates are soldered to the foil bridge.
 60. A device according to claim1, wherein the second contact pad is adapted to be mechanicallyconnected to the second body by a fixed mechanical, thermally conductivecontact.
 61. A device according to claim 28, wherein the first andsecond bendable regions include material-thinning grooves.
 62. A deviceaccording to claim 29, wherein the first and second contact pads and theat least one leg are comprised of plates and the first and secondbendable regions include a foil bridge.
 63. A device according to claim30, wherein the at least one leg includes a material-thinning groovethat extends diagonally across the at least one leg from said first endto said second end.
 64. A device according to claim 28, wherein thefirst and second contact pads and the at least one leg are comprised ofplates and the first and second bendable regions include a foil bridge.65. A device according to claim 37, wherein the first bendable regionincludes a foil bridge that holds together mutually adjacent plates on afirst side of the plates and the second bendable region includes a foilbridge that holds together mutually adjacent plates on a second side ofthe plates.
 66. A device according to claim 29, wherein the plate thatforms the legs is divided into two parts from the first end to thesecond end diagonally across said legs and and is a two-part plate, thetwo-part plate being held together by a foil bridge.
 67. A deviceaccording to claim 37, wherein the plate that forms the legs is dividedinto two parts from the first end to the second end diagonally acrosssaid legs and is a two-part plate, the two-part plate being heldtogether by a foil bridge.
 68. A device according to claim 42, whereinthe foil bridge is glued to the plates.
 69. A device according to claim42, wherein the foil bridge is soldered to the plates.
 70. A deviceaccording to claim 27, wherein the first contact pad is adapted tomechanically contact the first body with a fixed mechanical, thermallyconductive contact.
 71. A device according to claim 27, wherein thesecond contact pad is adapted to mechanically contact the second bodywith a slidable mechanical, thermally conductive contact.
 72. A deviceaccording to claim 48, wherein the second contact pad is adapted tomechanically contact the second body with a slidable mechanical,thermally conductive contact.
 73. A device according to claim 1, whereinthe first and second contact pads and the resilient element are formedfrom a single piece of material.
 74. A device according to claim 27,wherein the first and second contact pads and the resilient element areformed from a single piece of material.